The Moon's Phases in Oreos

Why does the Moon look different throughout the month?

Animation shows the Moon going through all its phases.

The Moon has "phases." That means it looks a little different to us each night during its one-month orbit of our planet. We describe how the Moon looks with terms such as "Full Moon," "First Quarter," and "New Moon" (which we can't really see, because the side that is lit faces away from us).

The Moon has no light of its own. Moonlight is sunlight bouncing off the Moon's surface. As the Moon orbits Earth, the Sun lights up whatever side of the Moon is facing it. To the Sun, it's always a full Moon! If you were looking down upon Earth and its Moon from way out in space over the North Pole, you would see a Moon that looked like one of these:

Top-down view of Earth  and Moon, with Sun in the distance. Four Moons are shown, equally space around Earth. Each moon is lit on only the side facing the sun.

But we see the Moon from the center of its orbit. So we see different portions of the lit side of the Moon.

Same image as above, but this one adds drawings of how the Moon looks at each position as seen from Earth.

article last updated July 11, 2018
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